1. Field of the Invention
The present invention relates generally to an apparatus for magnetically recording and/or reproducing audio and video signals, and more particularly, is directed to a magnetic recording and/or reproducing apparatus which is operative to record and/or reproduce a frequency-modulated audio signal, together with a video signal, in oblique tracks arranged successively on a magnetic tape by means of a rotary magnetic head.
2. Description of the Prior Art
In video tape recorders generally in use when recording a color television signal on a magnetic tape, chrominance and luninance signals that constitute a color video signal are separated, and the chrominance signal is frequency-converted to have a frequency band lower than the frequency band wherein an appropriate carrier is frequency-modulated by the luminance signal so as to produce a frequency-modulated luminance signal. The frequency-converted chrominance signal and the frequency-modulated luminance signal are mixed to form a processed color video signal that is recorded through two rotary magnetic heads on the magnetic tape in successive and parallel record tracks extending obliquely with respect to the running direction of the magnetic tape. In such a system for recording a color television signal, an audio signal is recorded through a stationary magnetic head on the magnetic tape in a separate audio track extending in the running direction of the magnetic tape.
In relation to such a recording system, it has been known to restrict the speed at which the magnetic tape is transported so that the oblique tracks are positioned to be immediately adjacent to each other, that is, so that the spaces or so-called guard bands between the adjacent oblique tracks will be eliminated, in order to increase the recording density of the processed color video signal on the magnetic tape, and thereby to increase the duration of the recording. In such a case, however, the problem of "cross-talk" between these closely arranged oblique tracks arises in the reproduction mode wherein the processed color video signal is read from the oblique tracks on the magnetic tape. This problem of cross-talk can be solved by providing the two rotary magnetic heads, which form the oblique tracks alternatively, with different azimuth angles so that a substantial azimuth loss is obtained in cross-talk components derived from the adjacent oblique tracks, and in addition, by causing the chrominance signal to be subjected to appropriate circuit treatments before being recorded on the magnetic tape and after being read from the magnetic tape.
When high density recording of the processed color video signal is effected as described above, the transport speed of the magnetic tape is necessarily quite low, and the desired relative velocity between the magnetic tape and the rotary magnetic heads is maintained by the rotation of the latter. Thus, the relative velocity between the magnetic tape and the stationary magnetic head, which records the audio signal in the audio track, is also quite low, with the result that the quality of the recorded audio signal is deteriorated.
It has been proposed that the audio signal be frequency-modulated and then mixed with the processed color video signal to provide a mixed signal supplied to the rotary magnetic heads for recording such mixed signal in the oblique tracks so as to prevent deteriorations in the quality of the recorded audio signal due to the low transport spread of the magnetic tape. In such recording system for recording a mixed signal, it is required that an arrangement be provided for eliminating substantially a beat that may appear in a reproduced audio signal as a result of cross-talk in respect to the frequency-modulated audio signal included in the mixed signals recorded in each two adjacent oblique tracks.
In the recording system wherein the frequency-modulated audio signal is recorded, together with the processed color video signal, in the oblique tracks on the magnetic tape, as shown in FIG. 1 in which the abscissa represents the frequency F and the ordinate represents the level L, a frequency-modulated audio signal Af which is obtained by frequency-modulating a carrier having a predetermined frequency by an original audio signal is arranged so as to appear in the relatively narrow space between the upper boundary portion of the frequency band of a frequency-converted chrominance signal Cc and the lower boundary portion of the frequency and of the lower side band of a frequency-modulated luminance signal Yf. A mixed signal which contains the frequency-modulated audio signal Af and a processed color video signal composed of the frequency-converted chrominance signal Cc and the frequency-modulated luminance signal Yf is supplied to the rotary magnetic heads and thereby recorded in the oblique tracks on the magnetic tape.
In such a case, a carrier frequency Fa of the frequency-modulated audio signal Af is selected to be, for example, 1.5 KHz and the width of the frequency deviation range thereof is determined to be, for example, 100 to 150 kHz. The frequency-modulated luminance signal Yf has a the frequency deviation range such that the leading edge of the synchronous signal portion of a luminance signal Y separated from an original color television signal corresponds to a frequency Fs of, for example, 4.2 MHz, while the white peak (the maximum amplitude) of the luminance signal Y corresponds to a frequency Fp of, for example, 5.4 MHz. The frequency-converted chrominance signal Cc is formed to have a color subcarrier frequency Fc of, for example, about 743 kHz. Further, the level of the frequency-modulated audio signal Af is set to be lower than the level of the frequency-converted chrominance signal Cd, which is lower than the level of the frequency-modulated luminance signal Yf.
When the above mentioned recording system is used for recording wherein the frequency-modulated audio signal in the oblique tracks on the magnetic tape together with the processed color video signal composed of the frequency-converted chrominance signal and the frequency-modulated luminance signal, deterioration of, the recorded audio signal due to the low transport speed of the magnetic tape is substantially avoided. However, in the case where two-channel audio signals such as left and right channel signals forming a stereophonic audio signal are recorded with the described recording system, two carriers having their respective frequencies spaced from each other by, for example, 150 kHz, are frequency-modulated by these audio signals, respectively, so as to produce two individual frequency-modulated audio signals, each of which has the width of the frequency deviation range determined to be, for example, 100 to 150 kHz, and which occupy an expanded frequency band between the frequency bands of the frequency-converted chrominance signal and frequency-modulated luminance signal. Consequently, the side bands of the frequency-converted chrominance signal and the frequency-modulated luminance signal are suppressed or narrowed to provide space for the expanded frequency band of the two frequency-modulated audio signals, so that the quality of the reproduced picture obtained in accordance with reproduced chrominance and luminance signals is deteriorated. Conversely, if the audio frequency band between the frequency bands of the frequency-converted chrominance signal and frequency-modulated luminance signal is restricted so as not to suppress the side bands of the frequency-converted chrominance signal and the frequency-modulated luminance signal, it is difficult to record two-channel audio signals in such restricted band.